From Killing Floor Wiki
A player who intentionally tries to disrupt or ruin other players' gameplay is known as a griefer. Some griefers try to make their intentions unclear so that they can harm the team indefinitely without being kicked.
 Griefing acts to majority of players
- Blocking Trader entrances.
- Unwelding or destroying doors that the team wants welded.
- Purposely running in front of an explosive weapons user to cause self-damage.
- Purposely enraging the Fleshpound with a weak weapon so that it will damage or kill its target.
- Being useless by following team-mates around for protection while not assisting them at all.
- Blocking players to prevent them from backpedaling away from specimens.
- Using a shotgun to knock team-mates off edges.
- Welding doors to block team-mates.
- Team-killing on purpose (on friendly fire servers).
- Firing explosives at specimens that are close to team-mates, creating opaque smoke clouds that may annoy players by obstructing their view.
- Kiting the final specimen indefinitely while the rest of the team is waiting at the trader for the round to end.
- Firing flamethrower at fleshpounds/scrakes and sirens, which will obstruct the view of the sharpshooter who could take them down quicker.
 Griefing acts to some players
- Abusing bugs.
- Spamming voice commands.
- Abusing players